1. Field of the Invention
The present invention relates to a light emitting device having a plurality of light emitting cells on a single substrate, and more particularly, to a light emitting device having an isolating insulative layer for isolating a plurality of light emitting cells from one another on a single substrate, and a method of fabricating the light emitting device.
2. Discussion of the Background
There have been developed light emitting devices operated under high-voltage and AC power for use in general illumination. Such a light emitting device has been disclosed in WO 2004/023568(A1) entitled “Light-emitting device having light-emitting elements” by Sakai et al.
The light emitting device has a plurality of light emitting diodes (hereinafter, referred to as light emitting cells) on a single substrate. The plurality of light emitting cells are connected in series and reverse parallel with one another through metal wirings so that they can be connected directly to a high-voltage and AC power source.
FIGS. 1 to 3 are schematic sectional views illustrating a method of fabricating a light emitting device having a plurality of light emitting cells according to a prior art, and FIG. 4 is a plan view of FIG. 2.
Referring to FIG. 1, a buffer layer 20, an N-type semiconductor layer 30, an active layer 40 and a P-type semiconductor layer 50 are sequentially formed on an entire surface of a sapphire substrate 10.
Referring to FIG. 2, the P-type semiconductor layer 50, the active layer 40, the N-type semiconductor layer 30 and the buffer layer 20 are patterned using photolithographic and etching processes such that a plurality of light emitting cell regions are isolated from one another. Further, portions of the P-type semiconductor layer 50 and the active layer 40 are etched such that a portion of the N-type semiconductor layer 30 can be exposed as shown by a dotted line. Therefore, as shown in FIG. 4, a portion of the N-type semiconductor layer 30 is exposed and a plurality of light emitting cells electrically isolated by trenches are formed on the substrate 10.
Referring to FIG. 3, a transparent electrode layer 60 is formed on the P-type semiconductor layer 50. The transparent electrode layer 60 of one light emitting cell is connected to the exposed N-type semiconductor layer 30 of another light emitting cell adjacent to the one light emitting cell through a conductive wiring 70.
Through the conductive wirings 70, arrays of the light emitting cells connected in series are provided on the substrate 10 and are connected in reverse parallel with each other, so that a light emitting device operating under an AC power source can be provided.
However, since the P-type semiconductor layer 50, the active layer 40, the N-type semiconductor layer 30 and the buffer layer 20 are patterned in the method of fabricating the light emitting device according to the prior art, the deep trenches are formed between the light emitting cells. Accordingly, particles may easily remain in the trench, and a process of forming wirings through which light emitting cells are connected to one another is difficult. Current leakage may occur between the light emitting cells due to the particles. Such current leakage reduces light emitting efficiency and results in device failure.
Meanwhile, since GaN-based light emitting devices emit short-wavelength light such as blue or ultraviolet light, it is necessary to implement mixed light, e.g. white light, by converting wavelength of the light emitted from the light emitting devices so that the light emitting devices can be used for general illumination. In particular, a light emitting device having a wavelength conversion material layer at a chip level is necessary to simplify packaging processes.